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should I ventilate my cathedral ceiling

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hello, in my living room, half of it is a cathedral ceiling and the other half is craw space. There are no vents on either end of the cathedral side. Also the the ceiling does not go all the way to the ridge, it is caped off. I do have a ridge vent on the entire house. From your article on cathedral venting, i should vent the these spaces with small vents or just leave it alone?   CARLOS
asked in Attic Area by carlos (120 points)
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1 Answer

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Hi Carlos,
 
It would depend on a type of insulation in a cathedral ceiling section and your climate zone. If you have a properly installed foam type insulation entirely filling rafter spaces above the ceiling; there’s no need (nor way) for ventilating it. If this foam insulation is a closed cell type it would work in warm and cold weather, however, if an open cell foam type insulation has been applied it could result in mold growth during cold season. 
 
Other common types of insulation used between the rafters, like fiberglass, utilize air between the fibers as an insulator. If you’re experiencing cold winters, condensation may develop between the fibers if there’s no ventilation space between the insulation layers sitting on the ceiling’s finishing material (drywall, paneling, etc.) and the roof decking material (plywood, wooden planks, etc.). In order for condensation to evaporate without (very often) causing mold growth is to provide air flow / circulation. 
 
If those rafter bays are sealed you may need to open one of them and check what’s inside. Let me know if you have more questions, just click “comment” below.
answered by darekrudy (21,730 points)
hello, sorry it took so long to get back to you!  Anyway i was able to get up in the attic and look. There is an opening about 3 in. on the attic side, with fiberglass insulation between the rafters. I put in a new cealing fan awhile back and having to run wire for it , it was easy to do because the insulation was not tight in there.So im thinking there is some king of space there. Should i put some kind of vent on the other end of the rafter? (towards the outside)

 

Hi Carlos,
 
I still don’t know your location / climatic zone so it’s hard to say how critical in your situation would be soffit vent installation. If your roof decking surface is clean, no mold or deterioration that could be resulting from inadequate ventilation, maybe you do have sufficient air flow. 
 
If there are no vents at the lower portion of the roof (drip edge vents, soffit vents) installing them will only make sense if there’s open space between the top of insulation and the decking surface. If you can verify that; opening the soffit would improve air circulation. 
 
There’s not much else I can say and I understand that you may not be able to confirm that all the rafter bays are open… I would base my decision on what to do next on observation of the attic conditions. If there are no problems, you may not need to improve anything. 
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